When harvesting grain (wheat, barley, etc.) with a combine, the straw separated from the grain is usually discharged onto the field at the rear end of the combine, either in the form of a swath to be later taken up by a baler for further processing, or in chopped form over the width of the cutting path. If the straw is to be further processed, the extent to which the straw is damaged during the threshing and separating process depends on the design of the combine and the adjustment thereof, in addition to the properties of the grain plants. Thus, an excessively small threshing gap can cause a higher content of broken straw than a larger threshing gap.
In many cases, the quality of the straw plays a large part in the further utilization, because heavily damaged straw is barely suitable for use as an insulating material in structures and for similar tasks. It would therefore be desirable to detect the quality of the straw by using automatic means that operate more objectively than a human assessor.
It was proposed for this purpose to scan the straw swath in front of a tractor by means of a LiDaR sensor, i.e. a laser beam distance meter scanning the swath in the transverse direction, in order to evaluate the average height of the swath and the standard deviation thereof, proceeding from the assumption that damaged straw forms a more compact swath than undamaged straw (B. Lenaerts et al., LiDaR sensing to monitor straw output quality of a combine harvester, Computers and Electronics in Agriculture 83 (2012), 40-44). Accordingly, the straw quality is derived directly from the swath height, which can lead to erroneous assessments in case of locally lower throughputs.
Mounting a rear camera on the combine was also proposed in the prior art, so that by means of a monitor connected to the camera, the operator can check from his working position whether the crop residue is being discharged properly (JP 2005 137 260 A, JP 2008 182 938 A). U.S. Pat. No. 6,119,442 A discloses a camera that is mounted on the straw outlet of an axial separating rotor and is used to detect lost grain in the straw. None of these combines provide monitoring or automatic detection of the straw quality.